Chrome: Google's chat feature is useful for sending quick IMs and starting video chat sessions, but you can only view it when you're on a Google page like Gmail. Google has released an official Chrome extension that detaches it from your browser, allowing you to view it no matter what web page you're viewing.

This extension has actually been out for awhile, but was Chrome OS only. Now, you can grab it for Chrome on other platforms, letting you carry on chats, make voice calls, and even start Google Hangouts right from your desktop (my personal favorite feature). It doesn't have support for phone calls with Google Voice, which is kind of a bummer—that would take this from "cool" to "fantastic"—but it's helpful all the same, especially if you're tired of switching back to your Gmail tab to chat. Hit the link to check it out.